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How We Measure LED Light Quality by CRI

Now everyone probably realizes that not all light bulbs are created equally. Of course, there are different types of light bulbs you got, incandescent, fluorescent and LED.

But did you know there are actually different types of quality of the light that is actually produced by each bulb, and you can actually measure it using something called CRI – color rendering index.

The first question: How can you possibly measure the quality of light isn’t that pretty subjective?

Well, it’s basically comparing the light, that is produced by a particular bulb to a natural light source, usually in this case the sun. And specifically we’re comparing, how that light reflects and reveals colors it shines on to, that we then see and we usually use the Sun as a reference, and it’s said to have a perfect 100 CRI and you can kind of see on the spectrum of light it produces. It’s relatively smooth, there are no big spikes or anything like that. It’s also a good reference, because that’s the light source that our eyes evolved under. So it’s probably better to use a natural light source for the better reference as opposed to an artificial one, that our eyes aren’t used to, maybe you could say.

Besides the Sun, the only other light source that would really be a hundred CRI is some sort of blackbody radiation emitting.

For example, that would just be a chunk of matter, that is ideal and does not reflect any light. It’s kind of a physics term, but when you heat it up, it emits a certain spectrum of light at a certain color temperature based on how hot it gets. That’s where you get the terms like 5,500K. 6500K is basically referring to the color temperature that would be emitted by an ideal blackbody of matter. At that temperature, one example of a blackbody emitting light source is an incandescent light.

It’s not obviously an ideal blackbody, which doesn’t really exist, but it’s close enough and incandescent lights actually have a 100 CRI. It just uses heated upon stand metal and you can see also on its light spectrum, that it’s very smooth, it’s obviously not exactly like the Sun.

Because it’s more shifted towards the red and infrared, but because it’s so smooth that there are no spikes or anything, so it produces very good color representation.

Now 100 is the highest CRI you can get, but there is really no lower limit. As a matter of fact, there are some light sources that are negative.

For example, low pressure sodium light bulbs are actually in the negative 40s typically, that’s because they really only produce one band of yellow light. It’s just a big spike and it’s monochrome, so if you shine that at something, it’s really gonna make everything look yellow, which is obviously completely inaccurate.

The only advantage of that type of light is that it is very efficient, so uses power even more efficiently than LEDs. But because it produces color so poorly, you really only see low pressure sodium lights in street lamps and outside, and that sort of thing like in Los Angeles up until recently where they switch to LEDs.

Where do LEDs and fluorescents stack up? It really depends on the individual bulb, the manufacturer. You can probably expect a CRI only of about 50, because if you look at the spectrum fluorescents typically have a big spike in the green, also in the orange.

So a lot of times if you use fluorescent lights on video for video lighting, it usually casts kind of a green cue that you have to edit out later. It’s not that big a deal, but it is there.

However, there are high CRI fluorescent lights. They use multiple different phosphors in the light, they get illuminated, so it more evens out the spikes.

It’s a higher CRI and it’s more uniform even though you still get the spikes. It is a better quality especially for video for LED lights. You usually see a higher CRI usually 80, or higher and that’s because it really doesn’t have any spikes like the fluorescents do, and also there are high CRI LEDs.

Some claim that they can go up to the high 90s like 97 CRI. That’s getting pretty close to tungsten incandescence, and they’re often used because they’re just so power efficient. It kind of gives a trade-off, a good trade-off compared to the really power-hungry incandescence.

What’s the point of having this measurement and why would you want a high CRI?

There are many places where you’d want a good light source. For example, if you have an art gallery. That’s obviously very important to have good color representation, because you know people want to go and see the colors used in the art, or whatever.

So you want a high CRI light so that you’re actually seeing what’s on the painting or whatever.

Also say you own a clothing shop and you are selling clothes and trying to show different colored shirts or something like that. The customers probably want to have a really good representation of the real color of that shirt or whatever. When they leave the store and go out in the sunlight, it doesn’t look completely different than what they expected. It probably wouldn’t look completely different, but you know what happened.

Anywhere, color is important to the location or situation, you probably want to have a good light source because color is all about the light source really.

Anyway, now CRI isn’t a perfect system, there are some cases where it’s not the best measurement, especially in cases where the color temperature of the light is less than 5,000 Kelvin. There are other color appearance models, that’s what they’re called then are less popular, but might be better in other situations.

For example, there’s one metric called TLC eye television lighting consistency index, which is specifically designed to represent how color is going to be revealed on video sensors. Not necessarily the human eye, because video sensors obviously use a completely different method of capturing light data than the human eye. You want that to be consistent because what you see might be completely different than what the video camera sees.

There are different models that might even be more accurate than CRI, but it’s still the most popular. The next time you go to buy light bulb and you see that one is way more expensive than the other, it might be produce better light. It’s something worth checking out maybe on the box, it might tell you the CRI or at least something you can look up later, or if you are doing some video work then you probably want to go for a higher CRI or even do some research. If you own a shop or something like that hopefully you found this idears useful and interesting.